Lubricant compositions



United States Patent Ofiice 3,230,168 LUBRICANT COMPOSITIONS Hans Low, Bonn, Germany, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 8, 1964, Ser. No. 416,830 4 Claims. (Cl. 252-33.6)

infrequently required to function at temperatures above 400 F., where known mineral oils deteriorate rapidly, become corrosive, and volatilize, thereby becoming useless for their intended purpose. Even synthetic base oils, such as esters, ethers, silicones or hydrocarbon polymers, often undergo thermal and oxidative degradation under these extreme conditions, resulting in sludge and deposit formation, viscosity change, discoloration, increased corrosivity, and other undesirable changes. Attempts to correct these deficiencies by conventional methods are often unsatisfactory because of the extreme nature of the application of the oil; for example, addition of an antioxidant to reduce deterioration may cause increased corrosion, or addition of an antiwear agent might decrease stability. Furthermore, attempts to remedy the new deficiencies frequently compound the problem by causing increased sludging, etc. Therefore, available information regarding mineral oil formulations is of little aid in developing successful synthetic lubricants.

'It has now been discovered that a combination of certain hydrocarbyl amine salts of N-substituted dithiocarbamic acid with certain aromatic amines provides an excellent antioxidant for synthetic ester oils. Although the dithiocarbamic acid salts (also referred to herein as ammonium dithiocarbamates) and the aromatic amines of the invention are individually known to be useful as lubricating oil additives, together they cooperate to provide unexpected resistance to oxidation and formation of insolubles. This combination has the further important advantage of being substantially non-ash-forming.

The amine salts of N-substituted dithiocarbamic acids to be used in the practice of the invention may be represented by the following formula:

where R and R are hydrocarbyl groups having 1 to 20, preferably 1 to 12, especially 1 to 8 carbons per group, and R and R are alkyl groups having 1 to about 12, preferably 1 to 8 carbons. The term hydrocarbyl is intended to mean a radical formed from a hydrocarbon by removal of a hydrogen atom, including alkyl, cycloalkyl, aryl, aralkyl, and alkaryl groups. Alkyl groups are preferred substituents. Representative hydrocarbyl groups include methyl, propyl, tert-butyl, isooctyl, cyclohexyl, phenyl, benzyl, ethylphenyl, and naphthyl. These carbamates are used in amounts of from about 0.01 to 5%, preferably 0.1 to 3% by weight of the final lubricating composition.

Examples of suitable ammonium carbamate salts for use in compositions of the invention are diisobutylammonium diisobutyl dithiocarbamate, neopentyl n butylammonium phenyl isobutyl dithiocarbamate, hexyl isoamylammonium benzyl phenyl dithiocarbamate, diiso- Patented Jan. 18, 1966 butylammonium diphenyl dithiocarbamate, and methyl isobutylammonium naphthyl phenyl dithiocarbamate. These salts are readily formed by mixing: the appropriate dithiocarbamic acid with the appropriate amine in the liquid phase at room temperature.

Suitable cyclic amines to be used in the amine-salt combination of the invention are primary to tertiary amines, each non-hydrogen substituent of which is a monoto di-nuclear unsaturated cyclic radical containing from 4 to 10 carbon atoms and from 0 to 2, preferably 0 to 1 nitrogen atoms. Primary to secondary, especially secondary, amines are preferred; the cyclic radicals are preferably aromatic. Included are aryl amines and amines having nitrogen containing heterocyclic substituents. Many of these amines are well known antioxidants for both synthetic and mineral lubricating oils. Examples of suitable aryl amines are phenyl-u-naphthylarnine, phenyl-,B-naphthylamine, diphenylamine, di-a-naphthylamine, di B naphthylamine, di-a,fi-naphthylamine, triphenylamine, and diphenyl naphthylamine. Examples of suitable amines having a nitrogen-containing heterocyclic constituent are dipyridyl amines, aminopyridines, aminoquinolines, etc. Specific examples include 2,2-dipyridylamine, Z-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2,6-diaminopyridine, 4,4'-dipyridylamine, phenyl-2- pyridylarnine, naphthyl-Z-pyridylamine, 3-aminoquinoline, and phenyl-3-quinolylamine. Preferred amines are phenyl-u-naphthylamine and diphenylamine, especially phenyl- 2naphthylamine. The cyclic amines are used in amounts of from about 0.01 to 10% by weight, preferably 0.02- 5% by weight of the final lubricating composition.

Amine salts of N-substituted dithiocarbamic acids and aromatic amines are by themselves relatively weak antioxidants. Together, however, these classes of compounds cooperate to impart remarkable oxidation stability to synthetic ester oils. To illustrate the effectiveness of the combination of the invention, air oxidation tests were conducted. In these tests, a stream of air (30 ml./ minute) was bubbled through a 20-gram sample of oil in the presence of 20 ppm. each of copper and iron octoate catalysts. The base oil used was an ester of penta-erythritol and C C alkanoic acids. The induction period, which is the length of time elapsed before a substantial increase in the rate of uptake of oxygen occurs, is a standard measure of oxidation stability and is tabulated below for each oil. Tests were conducted at 350 F. and 450 F Oxidation tests results TEST TEMPERATURE, 350 F.

Induction Inhibitor Cone, percent In. Catalyst, p.p.m. Period,

PhenyLa-naphthyl- 0.0025 (0.083% 20 Cu +20 Fe 210 amine (PAN). w. Diisobutylammom'um 0.0025 (0.055% do 144 diisobutyl dithiow.).

carbamate (DADDO). Neopcntyl-n-butylarn- .0025 (0.09% do 210 monium neopentylw.).

n-butyl dithiocarbamate (NBNDC).

DADDO PAN 0.0025 each do 1,750 NBNDC PAN 0.0025 each do 2,150

TEST TEMPERATURE, 450 F.

PAN None 70 PAN 20 Cu 20 Fe- 2 2-Dipyridylamine. 20 Cu 20 Fe.-. 300 Ili-n-butylammonium None 25 Di-n-butyldithiocarbamate (DDDC). DDDO PAN None 2, 400

20 Cu 20 Fe-.. 4 5 20 Cu 20 Fe 3 1,320 Dipyridylamine.

Sludge formation observed.

These results indicate that the combination of an ammonium dithiocarbamate with an aromatic amine successfully inhibits oxidation of a synthetic oil, whereas the individual components are relatively ineffective.

The additive combination of the invention is used in organic ester base oils. Preferred oils are esters of alcohols having 1 to 20, especially 4 to 12, carbon atoms and aliphatic carboxylic acids having from 3 to 20, especially 4 to 12, carbon atoms. The ester base may be a simple ester (reaction product of a monohydroxy alcohol and a monocarboxylic acid), a polyester (reaction product of an alcohol and an acid, one of which has more than one functional group), or a complex ester (reaction product of a polyfunctional acid with more than one alcohol, or of a polyfunctional alcohol with more than one acid). Also, excellent synthetic lubricants may be formulated from mixtures of esters, such as major proportions of complex esters and minor amounts of diesters.

Monohy-dric alcohols suitable for making ester base stocks include methyl, butyl, isooctyl, dodecyl and octadecyl alcohols. Oxo alcohols prepared by the reaction of olefins with carbon monoxide and hydrogen are suitable. Neo alcohols, i.e., alcohols having no hydrogens on the beta carbon atom are preferred. Examples of such alcohols are 2,2,4-trimethylpentanol-1 and 2,2-dimethyl .propanol.

Polyalcohols used for the production of base oil esters preferably contain 1 to '12 carbons. Examples of dialcohols are 2-ethyl-1,3-hexanediol, 2-.propyl-3,3-heptanediol, 2-butyl-1,3-butanediol, 2,4-dimesityl-1,3-butanediol, and polypropylene glycols having molecular weights of from .about 100 to 300. Alcohols having 3, 4, 5 or more hydroxyl groups per molecule are also suitable and are preferred; examples of these polyols are entaerythritol, dipentaerythritol, and trimethylolpropane. Mixtures of alcohols may also be used.

Suitable carboxylic acids for making the ester base oils include monoand di-basic aliphatic carboxylic acids. Examples of appropriate acids are butyric, valeric, sebacic, azelaic, suberic, succinic, caproic, adipic, ethyl suberic, diethyl adipic, oxalic, malonic, glutaric, penadecanedicarboxylic, diglycolic, thiodiglycolic, acetic, propionic, caprylic, lauric, palmitic, pimelic, and mixtures thereof. Preferred acids are sebacic, azelaic, glutatic, adipic, and their mixtures.

Examples of suitable ester base oils are ethyl palmitate, ethyl laurate, butyl stearate, di-(2-ethylhexyl) sabacate, di-(Z-ethylhexyl) azelate, ethyl glycol dilaurate, di-(2- ethylhexyl) phthalate, di-(l,3-methylbutyl) adipate, di (l-ethylpropyl) azelate, diisopropyloxylate, dicyclohexyl sebacate, glycerol tri-n-heptoate, di(undecyl) azelate, and tetraethylene glycol di(2-ethylene caproate), and mix- .tures thereof. An especially preferred mixture of esters consists of about 50 to 80% Wt. bis(2,2,4-trimethylpentyl) azelate and 20 to 50% Wt. 1,1,1-trimethylyl propane triheptanoate.

Especially preferred esters for use as base stocks in the present invention are esters of monocarboxylic acids having 3 to 12 carbons and polyalcohols such as pentaerythritol, dipentaerythritol, and trimethylolpropane. Examples of these esters are pentaerythrityl butyrate,

pentaerythrityl tetrabutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentaerythrityl dibutyratedicaproate, pentaerythrityl butyratecaproate divalerate, pentaerythrityl butyrate trivalerate, pentaerythrityl butyrate tircaproate, pentaerythrityl tributyratecaproate, mixed C saturated fatty acid esters of entaerythritol, dipentaerythrityl hexavalerate, dipentaerythrityl hexacaproate, dipentaerythrityl hexaheptoate, dipentaerythrityl hexacaprylate, dipentaerythrityl tributyratecaproate, dipentaerythrityl trivalerate trinonylate, dipentaerythrityl mixed hexaesters of C fatty acids and trimethyloypropane heptylate. Pentaerythritol estesr of mixtures of C C acids are excellent base oils, and are commercially available from Hercules Chemical Company.

Ester oils may be prepared by simple reaction of the alcoholic and acidic reactants in proportions suitable for producing the desired product; preparation preferably takes place in a solvent such as an aromatic hydrocarbon, and in the presence of catalyst, such as HCl, HF, HBr, H 50 H PO SOCI BF etc. Preparation of suitable esters is described in Eichemeyer, U.S. 3,038,859, issued June 12, 1962, and Young, U.S. 3,121,109, issued February 11, 1964.

I claim as my invention:

1. A lubricant composition comprising a major amount of a synthetic organic ester lubricating oil and (1) from 0.1 to 3% by Weight of an amine salt of N- substituted dithiocarbamic acid having the formula Where R and R are hydrocarbyl groups having 1 to 8 carbons and R and R are alkyl groups having 1 to 8 carbons, and

(2) from 0.2 to 5% by Weight of a diaryl amine.

2. A lubricant composition comprising a major amount of a synthetic organic ester lubricating oil, from 0.1 to 3% by Weight of diisobutyl ammonium diisobutyl dithiocarbamate, and 0.2 to 5% by weight of phenyl-alphanaphthylamine.

3. A lubricant composition comprising a major amount of a synthetic organic ester lubricating oil, from 0.1 to 3% by weight of di-n-butylammonium di-n-butly dithiocarbamate, and 0.2 to 5% by weight of phenyl-al pha-naphthylamine.

4. A lubricant composition comprising a major amount of a synthetic organic ester lubricating oil, from 0.1 to 3% by weight of dibutlyamrnonium diphenyl dithiocarbamate, and 0.2 to 5% by weight of phenyl-alpha-naphthlyamine.

References Cited by the Examiner UNITED STATES PATENTS 2,160,851 6/1939 Faust 25234 X 2,694,682 11/1954 Harle 25247 X 2,718,501 9/1955 Harle 252-47 3,151,076 9/1964 Epton et al. 25233.6

DANIEL E. WYMAN, Primary Examiner.

F, DEB A s ant Examiner. 

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR AMOUNT OF A SYNTHETIC ORGANIC ESTER LUBRICATING OIL AND (1) FROM 0.1 TO 3% BY WEIGHT OF AN AMINE SALT OF NSUBSTITUTED DITHIOCARBAMIC ACID HAVING THE FORMLA 